The invention relates to safety in electrical gear, and more particularly in air-insulated medium voltage switching kiosk substations that include current-limiting fuses.
Such kiosks are generally placed outside on a mount and they are used for distributing electricity at a voltage of less than 52 kV, which corresponds to the upper limit for medium voltage as standardized at the date of this application. It is not impossible that as fuse technology advances the voltages used in air-insulated switching kiosks will in the future exceed this value, in which case the invention will continue to apply in like manner to a range of voltages above 52 kV.
In such kiosks, each electricity feed bar is connected to an electricity distribution cable via a current-limiting fuse or a plurality of fuses placed side by side and connected in parallel in the circuit. Each fuse is said to be xe2x80x9cengageablexe2x80x9d, i.e. it is removably mounted so that it can be engaged or disengaged manually. Generally a medium-voltage switching kiosk has a hatch giving access to the fuses that enables an operator to disengage a blown fuse and replace it by engaging a new fuse. However during these manual operations of disengaging or engaging a fuse, the operator can be exposed to the risk of accident due to electric arcs. If a fuse is mounted in series with a vacuum-break switch, it is necessary for the switch to be open prior to the fuse being disengaged or engaged in order to prevent electric arcing.
Medium-voltage gear is known from U.S. Pat. No. 3,400,353 comprising a vacuum-break switch that can be mounted in series with a fuse. It is necessary for a door to be opened in order to access the fuse, the door being interlocked with the switch so that it can only be opened if the switch is open. A degree of safety is thus obtained by the device, providing the kiosk housing the gear is fitted with a door that is dimensioned so as to enable the operator to access the fuse.
An object of the invention is to make it safe to handle such engageable current-limiting fuses that are placed in a medium-voltage switching kiosk substation provided with a vacuum-break switch and having access to the fuses that can be constituted by a relatively small opening made in the kiosk, e.g. a hatch.
Another object of the invention is to be able to act on the drive mechanism of the switch with a tool that can also be used by the operator to disengage a terminal of a fuse, e.g. constituted by an insulating pole.
To this end, the invention provides a safety device for medium-voltage electrical gear comprising an electric circuit having a current-limiting fuse or a plurality of fuses placed side by side and connected in parallel in the circuit, and a vacuum-break current switch connected in series with the fuse and, in the closed position, carrying the permanent current of the electric circuit, the switch having a pair of contacts one of which is movable relative to the other, and a drive mechanism for moving the moving contact to open or close the switch, the mechanism being arranged so as to prevent the fuse(s) being disengaged or engaged while the switch is closed. In the device, the drive mechanism comprises a drive lever occupying a first position when the switch is closed and a second position when the switch is open, and wherein each fuse has a handle member which is masked by the lever when the fuse is engaged and the lever is in its first position, or uncovered when the lever is in its second position, the lever being designed to cover the handle member so as to mask it.
As a result, the operator is obliged to open the switch before handling a fuse, thus preventing any risk of accident by means of an electric arc. A vacuum-break switch is used to ensure that no electric arcing occurs in the air inside the electrical gear.
In a particular embodiment of the safety device of the invention, a portion of the lever is U-shaped, and the handle member of each fuse is formed by an eyelet masked by said portion of the lever when it is inserted between the two branches of the U-shape.
The eyelet of a fuse can advantageously be formed in a flange fixed to the fuse, said flange forming a finger which comes into abutment against the lever to prevent the fuse being engaged if the lever is in its first position.
In another embodiment, the drive mechanism is arranged in a manner that ensures that the switch is opened or closed fully and that the travel speed of the moving contact is correct, independently of the drive provided by the operator.